The present invention relates to conducting polymers and their use as electrodes in various devices, and, in particular, to certain bithienylnaphthalene- and bis(3,4-ethylenedioxythienyl)naphthalene-based monomers and polymers.
It is known that conjugated polymeric systems derived from regio-selective synthetic processes that preclude or minimize structural defects have shown, among other properties, much higher conductivity. A version of this approach is illustrated by the design and preparation of symmetrical conjugated monomers like bis(heterocycle-arylene) monomers, which upon electropolymerization, have led to polymers with minimal side reactions. Since these monomers and derived polymers are highly conjugated, they exhibit interesting and potentially useful luminescence characteristics. Most of the literature in poly(bis-heterocycle-arylenes) has focused on benzene as the arylene system. We have found that naphthalene as the arylene part provides more sites to modify the molecular structures of the monomers, and in turn, more control of the electronic properties of the derived polymers to satisfy the bulk property requirements.
It is an object of the present invention to provide novel monomers for the production of thin films and coatings useful in electrochromic applications.
It is another object of the present invention to provide polymers prepared by polymerization of these monomers.
Other objects, aspects and advantages of the present invention will be apparent to those skilled in the art from a reading of the following detailed disclosure of the invention.
In accordance with the present invention there are provided novel, electropolymerizable monomers of the formulae: 
wherein R1, R2 and R3 are selected from the group consisting of xe2x80x94H, xe2x80x94O(CH2)nCH3, 
wherein n has a value of 0 to 11 and m has a value of 1 to 4, and wherein no more than one of R2 and R3 is xe2x80x94H.
These monomers are synthesized by the palladium-catalyzed coupling reaction of 2-(tributylstannyl)thiophene or 2-(tributylstannyl)ethylenedioxythiophene with a naphthyl ditriflate or naphthyl dibromide as shown in the examples which follow. The coupling reaction works well in dioxane or toluene at reflux with tetrakis-(triphenylphosphine)palladium(O), Pd(PPh3)4.
These monomers are preferably electrochemically polymerized. Electrochemical polymerization of the above-described monomers can be carried out according to the methods generally employed for electrochemical polymerization of thiophene, pyrrole, and the like. The electrochemical copolymerization is carried out by cyclic voltammetry, by subjecting a mixture of monomer, solvent and electrolyte to one of the following conditions: (a) setting the potentiostat at a constant electrical potential where the monomer is optimally oxidized; (b) setting the potentiostat at a constant current value; or (c) repeated scanning between the redox potentials of the monomers. Typically, all three conditions are tested for a new monomer in order to select one as the optimal condition for achieving electropolymerized polymer films with the required stability and thickness. If the oxidation-reduction cycle can be repeated several times and the polymer film deposited on the electrode exhibits reproducible cyclic voltammetric (current-voltage) characteristics, it is then deemed to be electrochemically stable and well-behaved.
The solvents which can be used in the present invention may be either aqueous or nonaqueous, although a solution of the aforesaid electrolyte in a nonaqueous organic solvent is preferred. The organic solvents used herein are preferably aprotic and have high dielectric constants. For example, ethers, ketones, nitriles, amines, amides, sulfur compounds, phosphoric ester compounds, phosphorous ester compounds, boric ester compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds and the like can be employed. Of these, ethers, ketones, nitriles, phosphoric ester compounds, phosphorous ester compounds, boric ester compounds, chlorinated hydrocarbons and carbonates are preferred. Specific examples of suitable solvents include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, acetonitrile, proprionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1,2-dichloroethane, .gamma.-butyrolactone, valerolactone, dimethoxyethane, methylformate, propylene carbonate, ethylene carbonate, dimethylformamide, dimethyl sulfoxide, ethyl phosphate, methyl phosphate, ethyl phosphite, methyl phosphite, 3-methylsulfolane, etc. Among these, nitriles and carbonates are especially preferred in order to increase the response speed. These organic solvents may be used alone or in combination.
Specific examples of electrolyte which can be used in the present invention include tetraphenylarsonium chloride, tetraphenylphosphonium chloride, tetra(n-butyl)ammonium bromide, lithium bromide, tetra(n-butyl)ammonium hexafluorophosphate, and tetra(n-butyl)ammonium perchlorate (TBAP). These examples are merely illustrative and not limiting.
Within the context of the implementation of the process in accordance with the invention, the electrochemical reactions are advantageously carried out at the surface of an electrode. By measuring the current delivered during the reaction, the electrode effectively makes it possible to monitor the progress of the polymerization reaction (for example the thickness of the polymer formed) or the progress of subsequent reactions carried out on the copolymer.
The resulting polymers have the structures 
wherein R1, R2 and R3 are as previously defined and n is an integer indicating the degree of polymerization and having a value of at least 1. The ethylenedioxythiophene-containing polymers have similar structures.
The following examples illustrate the invention: